Internal Combustion Engine (2021) • Hacker News Board

Re: Internal Combustion Engine (2021)

#51

Post by aw1621107 » Wed, Jul 01, 2026, 8:38 PM UTC

duped wrote: post #46

This is a stupid question but I'm a stupid EE/SWE who knows very little about physical objects. In the all these animations of the pistons I see linear motion translated into rotary motion using the crank shaft - but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)? Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degree…

> but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)?

You can design the starter motor to ensure the engine always starts up moving in the right direction, and after that it's "just" a matter of timing (e.g., spark plugs controllled electronically in more modern cars, mechanically in older ones).

> Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degrees?

That's what the starter motor is for!

Re: Internal Combustion Engine (2021)

#52

Post by reorder9695 » Wed, Jul 01, 2026, 8:46 PM UTC

duped wrote: post #46

This is a stupid question but I'm a stupid EE/SWE who knows very little about physical objects. In the all these animations of the pistons I see linear motion translated into rotary motion using the crank shaft - but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)? Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degree…

The starter motor turns the engine in a defined direction, this acts as a turning force directly on the crankshaft so it doesn't matter where the crankshaft is. The pistons only start firing after the crankshaft is already moving.

It is actually possible for an engine to turn the wrong way, this occurs on motorbikes with kick starts. When you don't kick start it correctly (or if the ignition timing is way out), a piston can fire prematurely before top dead centre and force the crankshaft against the direction that the kick lever turns it, this is known as kick back and is about as fun as it sounds when the engine's force goes through the kick lever.

Re: Internal Combustion Engine (2021)

#53

Post by jabl » Wed, Jul 01, 2026, 8:48 PM UTC

duped wrote: post #46

This is a stupid question but I'm a stupid EE/SWE who knows very little about physical objects. In the all these animations of the pistons I see linear motion translated into rotary motion using the crank shaft - but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)? Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degree…

Some engines, nowadays mostly large marine diesels, are reversible. Change the valve timing, and start it in the opposite direction, and off it goes.

Re: Internal Combustion Engine (2021)

#54

Post by gwbas1c » Wed, Jul 01, 2026, 8:58 PM UTC

When I was a kid, pre-internet, my dad took me to the local library and checked out some books that explained how an engine works.

These animations are so much better than what I had!

Re: Internal Combustion Engine (2021)

#55

Post by raffael_de » Wed, Jul 01, 2026, 9:10 PM UTC

Toutouxc wrote: post #41

raffael_de wrote: post #32

Earlier quoted context omitted.

explosion/detonation causes engine knocking or pre-ignition which is both very bad. a properly working combustion engine is driven by controlled burning.

You’re replying to a post that says that “explosion” doesn’t imply “detonation”.

and that is not strictly correct. it's called combustion engine and not explosion engine for a reason.

Re: Internal Combustion Engine (2021)

#56

Post by vjvjvjvjghv » Wed, Jul 01, 2026, 9:14 PM UTC

This should probably be called “Four Strike Engine”. There are other types of ICE that work differently.

Re: Internal Combustion Engine (2021)

#57

Post by klaff » Wed, Jul 01, 2026, 9:20 PM UTC

gwbas1c wrote: post #54

When I was a kid, pre-internet, my dad took me to the local library and checked out some books that explained how an engine works. These animations are so much better than what I had!

When I was a kid we had a visible V8 model that let you see quite a bit!

Re: Internal Combustion Engine (2021)

#58

Post by Sohcahtoa82 » Wed, Jul 01, 2026, 9:23 PM UTC

throw567643u8 wrote: post #10

zuzululu wrote: post #6

[flagged]

Probably better for the environment too.

The carbon footprint of producing an EV is higher than an ICE. Nobody disputes that.

But the lower carbon footprint of operating the an EV makes the EV have a lower footprint over the life of the vehicle. This is true even if your electricity comes purely from coal, as a coal power plant gets an economy of scale that an ICE doesn't achieve. If your power comes from a renewable source, then the trade-off happens even sooner.

Re: Internal Combustion Engine (2021)

#59

Post by rootusrootus » Wed, Jul 01, 2026, 9:32 PM UTC

MarkusWandel wrote: post #12

Wonderful but it irritates me that so many descriptions of internal combustion engines refer to "explosions" of the fuel. You don't want that. It causes knocking and pinging and engine damage. You want a controlled burn that generates heat smoothly.

Even more confusing to anyone who doesn't know the lingo, detonation in the context of an internal combustion engine means something specific. It is a synonym for pinging and knocking, and happens when unburnt fuel/air mixture explodes after the spark plug has already fired. It can damage the engine, but typically takes some time. Preignition is when the mixture ignites before the spark plug fires, and is typically much more damaging, often destroying the engine in just a few revolutions. It can pound through the boundary layer between the mixture and the face of the aluminum piston and melt it, or break something else in the engine like a rod.

It's been a minute, but at one point GM had some pretty interesting videos up on YT where they talked about preignition testing on Cadillac Northstar V8s and how quickly it would grenade the engine. Fascinating stuff.

Re: Internal Combustion Engine (2021)

#60

Post by rootusrootus » Wed, Jul 01, 2026, 9:38 PM UTC

I still remember the first time I tore down a pushrod V8. I decided it had to be close to the pinnacle of elegant design. Nothing wasted, everything had a purpose, and it all came together in a perfect mechanical symphony. We have since made engines which are significantly more efficient and powerful, but all of that at the cost of elegance, slapping on overhead cams and machinery just to adjust the valve timing, etc. Fantastic technology in it's own right for certain, but feels tacked on, like an expensive optimization.

Reminds me that I want to get something for my kids to work on which will maybe show them some of that same elegance. I don't currently have any V8s in the garage to go tear down :)